The present invention relates to a method for the preparation of vinyl-containing macromers from olefins utilizing transition metal catalyst compounds with alumoxane co-catalyst activators.
Vinyl-terminated polymers, including for the purposes of this application oligomers, homopolymers and copolymers synthesized from two or more monomers, are known to be useful for post-polymerization (or post-oligomerization) reactions due to the available ethylenic unsaturation at one polymer one chain end or both. Such reactions include addition reactions, such as those used in grafting other ethylenically unsaturated moieties, and further insertion polymerization where the vinyl-terminated polymers are copolymerized with other monomers such as xcex1-olefins and/or other insertion polymerizable monomers. In this latter instance the vinyl-terminated polymers are often called macromonomers, or macromers.
Early work with metallocene transition metal catalyst compounds activated with alkylalumoxanes such as methylalumoxane led to observations that their use in olefin polymerization gave rise to unsaturated end-groups in a greater percentage of polymer produced than had typically been true of insertion polymerization using traditional pre-metallocene Ziegler-Natta catalysts. See EP-A-0 129 638 and its U.S. patent equivalent 5.324.800. Later work by Resconi, et al, reported in Olefin Polymerization at Bis(pentamethylcyclopentadienyl)zirconium and -hafnium centers: Chain-Transfer Mechanisms, J. Am. Chem. Soc., 1992, 114, 1025-1032, yielded the observations that the use of bis(pentamethylcyclopentadienyl) zirconcene or hafnocene in propylene oligomerization favors xcex2methyl elimination over the more commonly expected xcex2-hydride elimination as the means for chain transfer, or polymer chain termination. This was based on observations that the ratio of vinyl-end groups to vinylidene-end groups was in the range of 92 to 8 for the zirconocene and 98 to 2 for the hafnocene.
In addition to these observations, WO 94/07930 addresses advantages of including long chain branches in polyethylene from incorporating vinyl-terminated macromers into polyethylene chains where the macromers have critical molecular weights greater than 3,800, or, in other words contain 250 or more carbon atoms. Conditions said to favor the formation of vinyl terminated polymers are high temperatures, no comonomer, no transfer agents, and a non-solution process or a dispersion using an alkane diluent. Increase of temperature during polymerization is also said to yield xcex2-hydride eliminated product, for example while adding ethylene so as to form an ethylene xe2x80x9cend capxe2x80x9d. This document goes on to describe a large class of both mono-cyclopentadienyl and bis-cyclopentadienyl metallocenes as suitable in accordance with the invention when activated by either alumoxanes or ionizing compounds providing stabilizing, noncoordinating anions. The examples all illustrate the use of the Lewis acid activator tris(perfluorophenyl) boron with bis(cyclopentadienyl) zirconium dimethyl at a polymerization temperature of 90xc2x0 C. Copolymerization was conducted with ethylene and the two macromers, respectively., using the same catalyst systems as used to form the macromers.
Branched ethylene macromers are described in WO 95/11931. According to this disclosure vinyl groups are to be greater than 75 mol. %, more preferably greater than 80 mol. %, of the total unsaturated groups, and the weight average molecular weight is said to be in the range of 100 to 20,000. The method of manufacture of the described macromers is said to be with a transition metal compound containing metals of groups 3 through 10, cyclopentadienyl derivatives of group 4, 5, and 6 are said to be of satisfactory utility in this regard. These transition metal compounds are also said to capable of forming ionic complexes suitable for polymerization by reacting with ionic compounds, alumoxane or Lewis acids. The ratio of the transition metal component to the alumoxane component is said to be desirable when at 1/10 to 1/10,000, or most preferably 1/30 to 1/2000. Examples 1 and 7 illustrate ethylene macromer preparation with ratios of alumoxane compound to transition metal compound of 240 and 2000, respectively.
Various patents address the use of metallocene catalysts with varying levels of activating alumoxane cocatalysts. One such is U.S. Pat. No. 4,752,597 where relatively hydrocarbon-insoluble solid reaction products of metallocenes and alumoxane are prepared by reacting the two in a suitable solvent where aluminum metal to transition metal molar ratios are between 12:1 to 100:1. The solid reaction product is then removed. This solid reaction product is said to be useful for gas phase, slurry and solution polymerization.
Additional art addresses the preparation of chain-end unsaturated polymers with various metallocenes under various conditions, each of vinyl-, vinylidene-, vinylene- and trisubstituted-unsaturation resulting from the reported processes. The difficulty in determining by standard characterization methods (1H-NMR or 13C-NMR) the total of saturated chain ends has resulted in acceptance in the art of characterizing unsaturated end-group by the fraction of the total of each type of unsaturation to the total unsaturated ends. However, industrially efficient methods of production would greatly benefit from high unsaturated end group concentrations to the total end group population, that is including the saturated ends. Thus, the reported variations in molecular weight distributions and the inability to accurately determine or predict the resulting type of chain ends, or the less favored production of unsaturated chain-ends other than those of vinyl, limits the utility of the prior art. Vinyl-chain ends are generally accepted to be more reactive to chain-end functionalization and insertion in subsequent polymerization reactions than are the other types and are more highly preferred. Accordingly additional work was undertaken to improve the vinyl-chain terminated polymer preparation process, its predictability and its utility for use in the preparation of branched polymers.
The invention comprises an olefin polymerization reaction product having olefin unsaturation that is predominantly vinyl. In these reaction product compositions the molar concentration of vinyl groups is greater than or equal to 50% of the total polymer chain molar concentration. More specifically, as calculated from gel permeation chromatography (GPC) and differential refractive index (DRI) measurements, the invention is a polymeric reaction product composition of matter comprising olefin polymer chains having number-average molecular weights (xe2x80x9cMnxe2x80x9d) from about 400 to about 75,000, a ratio of vinyl groups to total olefin groups satisfying the formula                                           vinyl            ⁢                          xe2x80x83                        ⁢            groups                                olefin            ⁢                          xe2x80x83                        ⁢            groups                          ≥                                            [                                                comonomer                  ⁢                                      xe2x80x83                                    ⁢                  mole                  ⁢                                      xe2x80x83                                    ⁢                  percent                                +                0.1                            ]                        a                    xc3x97                      10            a                    xc3x97          b                                    (        1        )                                where        ,                  a          =                      -            0.24                          ,                              and            ⁢                          xe2x80x83                        ⁢            b                    =          0.8                                    xe2x80x83            
and, where the total number of vinyl groups per 1000 carbon atoms is greater than or equal to 8000÷Mn. It also includes a surprisingly, highly efficient method for preparing polymers having high levels of vinyl unsaturation comprising contacting one or more olefin monomers with a catalyst solution composition containing a transition metal catalyst compound and an alumoxane wherein the aluminum to transition metal ratio is from 10:1 to 220:1. Vinyl-containing chain yields at levels of greater than 70% of the total unsaturated chains can be achieved while simultaneously achieving high yields of unsaturated chains in the total polymer chains as calculated from GPC and NMR. Thus, use of the process conditions of the invention permits predictable macromer characteristics of both molecular weight and the vinyl unsaturation which further enable the preparation of branched polymers having tailored characteristics suitable for improved processing applications, for example where melt processing is either required or industrially preferred, and in polymer blends where the choice of macromer monomer or comonomer constituents can lead to improved compatibilities or other characteristics of the polymer blend.